M20B20 trouble

[petdej]

Hi, everyone.
First of all, I apologize, because it is an E28, not an E30, but considering the same engines, very similar electronics (Motronic 1.3), I ask for help because I have not been able to solve the problem for more than two weeks, after much time, patience, hard work and desperate attempts.
On forums dedicated to E28 I didn't find any help, too.
It is my old, trusty (at least it was until a few days ago !) E28 520i, 1987. M20B20 with Motronic 1.3 (172 ECU).
Here is tough one, I am afraid.
The problem that occurred about a month ago at first was occasional, to become more and more frequent and to last longer and longer, to finally become almost permanent and at last, permanent.
I will try to describe it as accurately as possible. While driving, there is a jerking, as if the engine partially stops working rhythmically every half a second/second. Driving is very difficult, practically impossible. At idle, there is also a rhythmic "choking" of engine operation. The tachometer in that rhythm shows a decrease in the number of RPM, and what is even stranger, the temperature gauge trembles slightly to the left in that rhythm, and the econometer (MPG gauge) strikes to the left (to zero), also in that rhythm. LPG conversion was done on the car, so the behavior is identical on both fuels (LPG and gasoline). What is interesting is that the relays for the fuel pump and for heating of the oxygen sensor click in the same rhythm. When a problem occurs, ECU lights a Check Engine and there is an error code 1264 (EGO Heater)-done by stomp test.
Replaced: ECU, AFM, CTS, Main relay, Fuel pump relay, Oxygen sensor heating relay, Oxygen (Lambda) sensor, CPS (Crankshaft position sensor), distribution cap and rotor, spark plugs, ignition cables, ignition coil. All connectors and grounds in the engine compartment have been cleaned and checked. Almost every cable and wire around has been checked by voltmeter and ohmmeter, for voltage and short circuit, etc.
No visible air (vacuum) leaks...
I have no more ideas. Help !

Here is video, first at idle, later at light throttle:

[petdej]

After countless attempts and lack of ideas, I started reviewing everything.
Upon careful inspection of the connector for the EVAP purge valve, on the inside (under the rubber insulation), I found traces of green oxide between the contacts.
Apparently, water once penetrated the connector and caused corrosion.
By measuring with an ohmmeter, the resistance between the contacts was of the order of a few ohms.
By cleaning the connector with a larger amount of contact cleaning spray, the oxide is completely removed and the connector is completely clean.
EUREKA!
Problem fixed !

Thank you all for your attention and support!

[Speedtouch]

Well done for sorting out the problem!

Any more pics of your E28?

[martauto]

Well done for sorting out the problem!

Any more pics of your E28?

Mart.

[petdej]

There is a few pictures of my E28...

[DanThe]

After countless attempts and lack of ideas, I started reviewing everything.
Upon careful inspection of the connector for the EVAP purge valve, on the inside (under the rubber insulation), I found traces of green oxide between the contacts.
Apparently, water once penetrated the connector and caused corrosion.
By measuring with an ohmmeter, the resistance between the contacts was of the order of a few ohms.
By cleaning the connector with a larger amount of contact cleaning spray, the oxide is completely removed and the connector is completely clean.
EUREKA!
Problem fixed !

Thank you all for your attention and support!

How strange, you should be able to unplug the valve and have no issues, ive seen similar problems with engines cutting out on E28's because of bad contacts in the engine loom to fusebox plug, very poor design

[petdej]

Hello.
Indeed, not so strange. With unplugged valve there is no issue, but problem is on connector side, between contacts, almost short circuit due to oxide trace. For ECU, it is overload, obviously.